JPH11199524A - Melt crystallization of wall surface falling type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the purification of a crude liquid organic compound in a higher purity by reduced steps comprising depositing the thin crystal film of the highly pure liquid organic compound on a wall surface as a seed crystal and subsequently supplying the crude liquid organic compound to the wall surface to grow the crystal. SOLUTION: The thin crystal film of a highly pure liquid organic compound is preliminarily deposited on a wall surface as a seed crystal, and the crude liquid organic compound is supplied to the wall surface to grow the crystal. Concretely, for example, 1,4-butanediol having a purity of 100% and supplied into a storage tank VI is circulated to a crystallization device 1 to wet its wall surface, and the circulation is stopped. A cooling medium cooled at a temperature not higher than the freezing point of the 1,4-butanediol is supplied to crystallize the thin film on the wall surface 2. Crude 1,4-butanediol is further supplied from the storage tank VI to the crystallization device 1 to flow down and simultaneously cool the supplied crude 1,4-butanediol on the wall surface 2. The deposited crystal is subsequently melted with a heating medium obtained by heating the cooling medium at a temperature not lower than the melting point of the crystal, and recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wall-fall type melt crystallization method. More specifically, the present invention relates to an improvement in a wall-fall-down type melt crystallization method using seed crystals precipitated on a wall surface. According to the method of the present invention, a high-purity liquid organic compound can be efficiently obtained with a smaller number of stages than the conventional method.

[0002]

2. Description of the Related Art A variety of melt crystallization methods using a wall-fall type apparatus instead of distillation to purify a liquid organic compound have been proposed (JP-A-5-132441). In this case, the purity can be increased by slowly growing the crystal in the initial stage and smoothing the crystal surface.

[0003]

However, in the case of the above-mentioned method, in the actual operation, the operation is often performed at a relatively large supercooling temperature and a high flow rate due to the relation between the operation time and the throughput. As a result, the surface roughness and the amount of impurities taken in at the beginning are increased, and it is necessary to increase the number of stages in order to obtain the desired purity. The present invention
It is an object of the present invention to provide a melt crystallization method capable of purifying a crude liquid organic compound with a smaller number of stages and higher purity.

[0004]

Means for Solving the Problems As a result of intensive studies in view of the above circumstances, the present inventors have deposited a crystal thin film of a high-purity liquid organic compound as a seed crystal on a wall surface and supplied a crude liquid organic compound thereto. By growing the crystal, it is possible to prevent the mother liquor from being mixed at an early stage where the impurity concentration is high, and to cause crystal precipitation and slow growth even in a region having a low supersaturation degree. Therefore, it is possible to establish a purification method with higher purity than the conventional method. That, also found that it is a very effective technology even in the case of crystallizing raw materials having a composition that is difficult to separate during sweating with high viscosity,
The present invention has been completed.

That is, the gist of the present invention is that a crystal thin film of a high-purity liquid organic compound is previously deposited on a wall surface, and a crude liquid organic compound is supplied to the wall surface to grow a crystal. Mold crystallization method. Hereinafter, the present invention will be described in detail.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The liquid organic compound to be used in the present invention is not particularly limited as long as it can be applied with a wall-falling-type melt crystallization method. 4-butanediol, acrylic acid, bisphenol A and the like. The high-purity liquid organic compound has a purity of usually 99 to 100% by weight, preferably 99.5 to 100% by weight, and more preferably 100% by weight.
Means The crude liquid organic compound refers to a compound having a purity of usually 85 to 99% by weight, preferably 90 to 99% by weight. Hereinafter, 1,4-butanediol, acrylic acid, and bisphenol A will be described as examples.

(1) The crystallization apparatus used in the present invention basically comprises a crystallizer, a storage tank and a liquid feed pump.
The cooling surface of the apparatus to be used may be any of a flat plate type and a tubular type as long as the liquid material (crude liquid organic compound) can flow down the wall surface. At the upper part of the wall surface, there is provided a raw material supply device serving as raw material supply means for causing the liquid raw material to flow down into a thin film on one surface side of the wall plate via the vertical surface. On the other side of the crystallization plate, there is provided a refrigerant supply pipe as a refrigerant supply means for causing a refrigerant having a temperature equal to or lower than the freezing point of the liquid raw material to flow down into a thin film. The refrigerant supply pipe also serves as a heat medium supply pipe for supplying a heat medium having a temperature equal to or higher than the freezing point of the liquid raw material to the other surface of the crystallization plate.

The liquid raw material is circulated and supplied by a pump, while the refrigerant flowing down on the other side of the crystallization plate is circulated and supplied to a refrigerant supply pipe via a pump and a cooler. The refrigerant referred to herein is a temperature below the freezing point of the liquid organic compound minus 40.
It is a liquid that can be cooled down to ° C. and heated above the freezing point. Specifically, 1,4-butanediol and acrylic acid are 30 to 40% by weight ethylene glycol, and bisphenol A is a silicone oil that can withstand up to 200 ° C.

(2) A high-purity liquid organic compound is circulated and supplied to one side of the crystallization plate and flows down into a thin film in such a crystallizer. The wall temperature at this time is room temperature. Circulate until the entire surface of the wall is wet. After confirming that the entire surface is completely wet, stop the circulation and allow to stand still.

(3) After standing, in a state where a thin film of the high-purity liquid organic compound is present on the wall surface, a refrigerant having a temperature equal to or lower than the freezing point of the liquid organic compound is allowed to flow down into a thin film on the other surface of the crystallized plate. The upper limit of the flow rate of the refrigerant is not limited as long as the flow rate of the thin film can be obtained. The higher the flow rate, the higher the heat transfer coefficient and the higher the processing speed.

(4) About 100 μm of high-purity liquid organic compound
After confirming that the thin film having a thickness of m has crystallized, the crude liquid organic compound is cooled while flowing down the wall surface to precipitate crystals of the liquid organic compound on one surface side of the plate. The supply temperature of the crude liquid organic compound is such that if the cooling temperature is too low in the presence of a high purity crystal as a seed crystal, the crystal is precipitated at once,
In the initial stage, the freezing point is preferably within + 5 ° C, more preferably within + 3 ° C. Specifically, in the case of 1,4-butanediol, preferably 14 to 17 ° C., more preferably 17 to 19 ° C., and in the case of acrylic acid, preferably 5 to 7 ° C.
° C, more preferably 7 to 9 ° C, and in the case of bisphenol A, preferably 160 to 163 ° C, more preferably 16 to 16 ° C.
3 to 165 ° C. Since the crystal surface cannot maintain the initial temperature due to a decrease in heat transfer efficiency due to crystallization heat or crystal thickness, the cooling temperature is gradually lowered in consideration of the rise in crystal surface temperature. After the thickness of the crystal layer reaches a predetermined value, the mother liquor is extracted from the circulation supply system. However, if the crystal layer is too thick, the thermal conductivity becomes worse and the crystallization time becomes longer, which is not efficient. Therefore, the thickness of the crystal layer is preferably about 3 to 7 mm.

(5) Thereafter, the temperature control medium is heated by a superheater to a temperature higher than the freezing point of the liquid organic compound crystal to form a heat medium, and the heat medium flows down to the other surface of the crystallizing plate. Then, along with the flow of the heat medium, the crystal melt of the liquid organic compound already obtained is heated to flow down to one surface side of the crystallization plate. As a result, the crystal of the liquid organic compound is heated from both sides and melts in a short time.

(6) In performing the above crystallization operation, it is preferable to perform a sweating operation in order to perform partial melting before melting the crystal. What is a sweating operation? This is for melting and removing a liquid having a high impurity concentration taken in between the precipitated crystals or adhering to the crystal surface, and is performed to further lower the impurity concentration of the crystals. Specifically, before a heat medium having a temperature higher than the freezing point of the crystal flows down to the other surface of the crystallized plate, a heat medium having a temperature close to the melting point of the target pure substance flows down in a thin film form to the other surface of the plate. This is done by partially melting the crystal. Therefore, when the crystal is partially melted by the heater, the sweating operation can be performed by heating the heat medium to a temperature lower than the melting temperature, so that the impurity concentration in the melt can be further reduced. it can.

[0014]

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples unless it exceeds the gist. Example 1 (1) The crystallization apparatus shown in FIG. 1 was used as an experimental apparatus, and crystallization was performed using 1,4-butanediol as a raw material among high-purity liquid organic compounds. A vertical plate type was used as a crystallizer. The size of the crystallization plate is 10mm wide and 600m high
m, and a transparent acrylic plate was installed on the side surface and the entire surface of the crystallizer to make it visible. As the refrigerant, a 30 to 40% by weight aqueous solution of ethylene glycol was used.

(2) 100 g of a 100% by weight solution of 1,4-butanediol is supplied to the storage tank V1. The raw material sent to the storage tank V1 is further sent to the crystallizer 1. Circulate the raw materials and wet the wall. (3) After confirming that the wall surface is wet, stop the circulation and allow to stand still. And, from the storage tank V1, 1,4-butanediol 10
Withdraw 0% by weight solution.

(4) A coolant set at a temperature below the freezing point of 1,4-butanediol is supplied to crystallize the liquid film on the wall surface. (5) 250 g of crude 1,4-butanediol having a purity of 94.35% by weight of the crystallization raw material is supplied to the storage tank V1. Storage tank V1
Is cooled to a predetermined temperature and then sent to the crystallizer 1. The raw material is circulated to the crystallizer under predetermined conditions to crystallize 50 g. After the remaining 200 g of mother liquor is sent to the storage tank V1, it is extracted from the bottom. Next, 10 g of the perspiration is perspired, and the perspiration liquid is sent to the storage tank V1, and the perspiration is extracted in the same manner as the mother liquor.

(6) Next, the purified crystal on the wall surface is melted by supplying a cooling liquid having a melting point or higher, and is recovered in the storage tank V1. (7) Despite the single-stage crystallization of the purified melt in the storage tank V1, the 1,4-butanediol composition is about 98% by weight or more.

Comparative Example 1 Crude 1,4-butanediol having a purity of 94.35% by weight was directly crystallized in one step, and only 1,4-butanediol having a purity of 95.6% by weight was obtained.

[0019]

According to the present invention, it is possible to efficiently recover a high-purity liquid organic compound with a smaller number of stages by using a melt crystallization purification method in which a seed crystal is precipitated on a wall surface.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one example of a wall-fall type melt crystallization apparatus used in the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crystallizer 2 Acrylic plate V1 Storage tank 3 Stirrer blade 4 Pump

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C07C 57/07 C07C 57/07

Claims (3)

[Claims] 1. A wall-falling-type melt crystallization method, wherein a crystal thin film of a high-purity liquid organic compound is previously deposited on a wall surface, and a crude liquid organic compound is supplied to the wall surface to grow a crystal. 2. The method according to claim 1, wherein the liquid organic compound is 1,4-butanediol, acrylic acid or bisphenol A. 3. The method according to claim 1, wherein the liquid organic compound is 1,4-butanediol.